1. Field of the Invention
The present invention relates to a vehicle communication system for conducting data communication between controllers. More particularly, the present invention relates to an abnormality detecting device for detecting a communication abnormality in a vehicle communication system, which comprises controllers controlling a vehicle and a diagnosis unit reading out data to be processed in those controllers.
2. Related Art
A vehicle communication system is available that conducts communication, through a bus, of common data between a plurality of controllers performing various controls of a vehicle. In such a system, an abnormality detecting device receives controller answers to transmitted data, and the system determines the presence of an abnormality in the communication system when no answer is received within a predetermined time after data transmission. There is also known the connection of a diagnosis unit for performing communication through a bus with the controllers with a view to reading out the history of the control status of the vehicle by the controllers.
In a vehicle communication system having such controllers as described above, the diagnosis unit is connected to the controllers when reading out vehicle abnormality data stored in the controller by a dealer, for example. This is problematic in that the controller cannot determine the connection of the diagnosis unit, and therefore abnormality detection based on answer back as described above is not applicable.